Umbilicus rupestris

Taxonomy 

Synonyms:

Umbilicus pendulinus DC.

Cotyledon umbilicus-veneris auct.

The scientific name comes from the navel-shaped leaves, and its habit of growing on rocks.

Its common name is Navelwort.

Chromosome No.: 2n = 48 (Stace 2010).

Umbilicus rupestris

Photography: A.J. Lockton

Distribution 

Umbilicus rupestris has a remarkably westerly distribution in Britain, occurring mainly in Wales, the south-west of England and the Clyde Islands of Scotland. In Ireland it is widespread, except in the most inland places and parts of the east coast. Its distribution is presumably largely governed by rainfall and humidity; however, it is a lowland plant and it is absent from the north, so temperature may also play a part. Although the New Atlas shows U. rupestris as declining slightly, this is not apparent from the Maps Scheme maps, although the data is still too patchy to be sure. If anything, there appears to be an expansion of its range, but whether that is due to deliberate planting or is possibly climate related is not yet apparent.

Ecology 

The substrate on which it grows is an attribute that seems worthy of investigation. In the Flora of Shropshire (Sinker et al. 1985) it is described as growing on sandstones, siltstones and dolerite, but avoiding limestone and quartzite. Grose (op. cit.), however, says it grows on limestone walls in Wiltshire. In the Floras of Cornwall (French, Murphy & Atkinson 1999) and Dorset (Bowen 2000), it is said to sometimes occur as an epiphyte on trees. Bowen mentions Fraxinus excelsior specifically as the host, although that was based on just one observation. In Shropshire it grows on rock outcrops in U1 Festuca ovina grassland at Haughmond Hill; in recent W8 Fraxinus excelsior woodland at Earl’s Hill; and in W16 or W17 Quercus petraea woodland at Oaks Wood. The NVC books (Rodwell 1991) only list U1. At Haughmond Hill, plants re-grew quickly after a fire in 2005.

Predators

The larva of the hoverfly Cheilosia semifasciata mines the leaves of U. rupestris and sometimes causes the collapse of entire plants by the autumn. This invertebrate was considered rare, but has turned up in a few new sites recently and would be worth looking out for. The maps produced by the Hoverfly Recording Scheme show current recording levels. This is apparently the only Navelwort leaf miner in Britain, so it is fairly easy to record.

Umbilicus rupestris and Cheilosia semifasciata

Cheilosia semifasciata larva.

Photography: N. Jones

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Status 
  • Origin: native in the west of Britain and in Ireland, but unknown in some parts of the east (see Further Work).
  • Rarity: common.
  • Threat: not threatened.
  • Conservation: it is not officially on any conservation list, but half a dozen county recorders have listed it as an axiophyte.
Further Work 

One unresolved question about this species is its status away from its core populations. The New Atlas (Preston, Pearman & Dines 2002) gives a few red dots in the east, claiming that these are introduced plants. This seems to be based on the assertion in Beckett & Bull’s (1999) Flora of Norfolk that a single plant at Sisland Carr (TM39) may have been planted. The old Fl. Norfolk (Petch & Swann 1968) does not list this species, which adds some weight to that assertion.

In the Flora of Wiltshire (1957), Donald Grose describes U. rupestris as native or denizen, where a denizen is a plant that has colonised man-made habitats but would not occur otherwise. He mentions just one instance of the plant on a hedgebank; otherwise it was found only on stone walls. Wiltshire is on the edge of its range, and Grose describes how plants in the east of the county are smaller and more sparse.

The Maps Scheme maps show that U. rupestris is recorded in scattered locations almost throughout the British Isles, from East Kent to Aberdeenshire. It would be worthwhile collecting observations about its origin in these places. If it is deliberately planted, does it persist? Or are these scattered colonies ‘denizens’ or colonists rather than genuine introductions?

References 
  • Beckett, G., Bull, A. & Stevenson, R. 1999. A Flora of Norfolk. Privately published.
  • Bowen, H. 2000. The Flora of Dorset. Pisces Publications, Berkshire.
  • French, C.N., Murphy, R.J. & Atkinson, M.G.C. 1999. Flora of Cornwall. Wheal Seton Press, Camborne.
  • Grose, J.D. 1957. The Flora of Wiltshire. Wiltshire Archaeological and Natural History Society, Devizes.
  • Petch, C.P. & Swann, E.L. 1968. Flora of Norfolk. Jarrold & Sons Ltd. Norwich.
  • Sinker, C.A., Packham, J.R., Trueman, I.C., Oswald, P.H., Perring, F.H. & Prestwood, W.V. 1985. Ecological Flora of the Shropshire Region. Shropshire Trust for Nature Conservation, Shrewsbury.
Citation 
Lockton, A.J. (date accessed). Species account: Umbilicus rupestris. Botanical Society of the British Isles, www.bsbi.org.uk.

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